The present invention relates to plastic injection molding systems and more particularly to gas injection pin mechanisms for such systems.
There are numerous known systems for plastic injection molding which utilize a gas to assist in the molding operation. In conventional plastic injection molding systems, plastic pellets are melted in an injection molding machine and advanced by a screw ram into a mold cavity. The mold cavity is formed between two mold halves (a core member and a cavity member), typically through one or more sprue bushings, a manifold and/or a hot runner system. The two halves of the mold are clamped, typically under high pressure, and the plastic is injected into the mold cavity, again under significant pressure in most instances. The molten plastic material in the cavity is allowed to cool and harden in the cavity, typically by a cooling system which circulates a cooling fluid through one or more of the mold members. When the part has sufficiently hardened, the mold is opened and the part is removed, typically by one or more ejector pins.
One of the known systems for utilizing a gas in an injection molding system is commonly known as xe2x80x9cgas-assisted injection molding.xe2x80x9d In these systems, the gas is injected into the molten plastic material through the plastic injection nozzle itself, or through one or more pin mechanisms strategically positioned in the mold, sprue bushings, manifold or hot runner systems. It is also possible to inject the gas directly into the molten plastic in the barrel of the injection molding machine. The gas, which typically is an inert gas such as nitrogen, is injected under pressure and forms one or more hollow cavities or channels in the molded part. The benefits of gas-assisted injection molding processes are well-known, and include the cost savings through the use of less plastic material, producing parts which are lighter in weight, and producing parts which have better surface definitions and finishes.
Another plastic injection molding system which utilizes gas injects the gas into the mold cavity along one or more exterior surfaces of the molded part. The pressurized gas forces the plastic against the opposite surface or surfaces of the mold cavity and forms a part with superior surface characteristics on the appearance surfaces.
There are a number of known systems and mechanisms for introducing the gas into the mold cavity, or melt stream. Many of these utilize moveable or stationary pin mechanisms. These mechanisms selectively introduce gas in or around the pin mechanism as needed for the particular injection molding system being utilized. Pin mechanisms of this type are shown, for example, in U. S. Pat. Nos. Re. 35,705, and 6,042,354.
Although many of these pin mechanisms are satisfactory and work well in their respective operations and systems, there is still a need for improved pin mechanisms for introducing gas into injection molding mechanisms and systems.
It is an object of the present invention to provide improved pin mechanisms for introducing gas into plastic injection molding mechanisms and systems. It is a further object of the present invention to provide stationary and/or moveable pin mechanisms which can be easily and inexpensively introduced into the mold or associated equipment, without the need for expensive machine operations or sleeve members.
In accordance with the present invention, various pin mechanisms are utilized by which can be directly inserted into bores in mold members, manifolds, hot runner systems or the like in order to introduce gas under pressure into the molten plastic in an injection molding system. In first embodiments of the present invention; stationary pin members are positioned directly in holes or bores in a mold member or the like and provide an annular discharge of gas into the mold cavity or molten plastic. As an alternate embodiment, the height of the stationary pin member in the mold member or related member can be adjusted.
In other embodiments of the present invention, moveable pin members are provided with or without mounting sleeve members. In one of these embodiments, gas is injected through a series of holes positioned around the perimeter of the pin member adjacent its outer end. In another of these embodiments, the pin member is lowered allowing gas to be injected in a solid stream.
Other embodiments, benefits, and features of the present invention will become apparent from the following description of the invention when viewed in accordance with the accompanying drawings and appended claims.